The present invention relates to methods and apparatus for addressing pixels in a display. More particularly, the present invention relates to methods and apparatus for addressing pixels in a display using one or more moving mechanical scanning mechanisms. The one or more movable mechanical scanning mechanisms (also referred to herein as xe2x80x9cmoving addressing elementsxe2x80x9d) and one or more stationary addressing elements provide electrical field addressing for control of the desired pixel(s) in a display.
Many types of display mechanisms have been described in the prior art that are addressed with electrical or magnetic fields (e.g., U.S. Pat. No. 6,017,584, U.S. Pat. No. 5,961,804, U.S. Pat. No. 4,126,854 are some examples). It is often desired to use these mechanisms to fabricate a display composed of rows and columns of pixels. However, even with fairly low-resolution applications, the total number of pixels quickly becomes very large. In higher resolution applications such as displaying a page of text, for example, the number of pixels can easily exceed 1 Million, 10 Million, or even 100 Million or more. It is generally infeasible to provide individually-controlled electrode and addressing electronics for each individual pixel in such a display.
Instead of individual control electronics for each pixel, such displays typically utilize an X-Y grid of electrodes. A typical prior art X-Y electrode addressing grid is illustrated in FIG. 1. Typically, strips of conductors 30 oriented in one direction (for example, along the rows of pixels) are fabricated on one side of the display 10 and strips of conductors 20 oriented in the opposing direction (along the columns of pixels) are fabricated on the other side of the display. In this manner, the number of control circuits is reduced from the product of the number of rows and columns to the much smaller sum of the number of rows and columns.
The X-Y electrode arrangement can thus apply an electric field to any pixel in the array. However, a problem with such an arrangement is that the strips of conductors also run past other pixels in the same column or row of the array. Due to the capacitance or resistance of each pixel, the voltage on a conductor wire may be coupled through the pixels being addressed to electrodes other than the pixels being actively driven. These other electrodes will then produce weaker electric fields .or current flow on other pixels in the array. The time spent actively driving a given pixel is very small compared to the amount of time the pixel is influenced by the weaker fields leaking during addressing of other pixels. The performance of the display is drastically reduced if not completely infeasible due to the leaking of electric fields.
The prior art solution to this problem has typically been to design one of three mechanisms into each pixel.
If each pixel has a hard threshold that needs to be exceeded before it will switch, the field strength of the secondary leakage can be designed to be lower than this threshold, such that the pixels which are not being addressed will stay as they are. The pixels to be changed are addressed with a field strength higher than this threshold. As an example, U.S. Pat. No. 4,126,854 describes how this may be accomplished using static versus dynamic friction in a twisting ball display. Many types of LCD displays also exhibit such threshold switching properties.
Even if each pixel cannot be made to have a hard-and-fast threshold, various types of non-linearities in the pixel response can be exploited to overcome the problem of fields coupling into the non-driven row and column wires.
If each pixel can be electrically fitted with a semiconductor diode or even a transistor, the problem is circumvented. The issue is of course how to economically fabricate a display with millions of diodes or transistors incorporated into it. This problem has been solved in the art of LCD displays and is commonly referred to as an active matrix LCD. This technique cannot always be applied to other display technologies due to material and processing constraints being incompatible with the material and processes required to fabricate the transistors. One main limitation of the process used to fabricate the transistors is that the high temperatures used are incompatible with substrates like polycarbonate or other plastics. For this and other reasons, this technique is commonly limited to silicon, glass, or ceramic substrates.
It would be advantageous to provide a technique for addressing pixels in a display which avoids the problem of leakage of electric fields or currents affecting pixels that are not being addressed. It would be further advantageous to provide for the addressing of pixels without the difficulty and expense of requiring a non-linear response or switching elements at each pixel in the display.
The present invention provides methods and apparatus having the aforementioned and other advantages.
The present invention relates to methods and apparatus for addressing pixels in a display. More particularly, the present invention relates to methods and apparatus for addressing pixels in a display using one or more moving mechanical scanning mechanisms. The one or more movable mechanical scanning mechanisms (xe2x80x9cmoving addressing elementsxe2x80x9d) and one or more stationary addressing elements provide electrical field addressing for control of the desired pixel(s) in a display.
In an illustrated embodiment of the invention, one or more strips of stationary addressing elements are arranged in a first direction on a first side of a display. One or more moving addressing elements are arranged in a second direction on a second side of the display. The one or more moving addressing elements are positioned adjacent an array of pixels in the display which contains the pixel(s) to be addressed. A pixel actuation field is established between the one or more moving addressing elements and the strip(s) of stationary addressing elements substantially adjacent the pixel(s) to be addressed in the display.
The pixel actuation field may be an electric field, where the one or more moving addressing elements are maintained at a fixed voltage potential. The electric field may be established by applying either a positive voltage or a negative voltage to the stationary addressing element(s) that intersect with the one or more moving addressing elements adjacent the pixel(s) to be addressed.
The one or more moving addressing elements may be driven by a belt-follower and pinion drive system, a lead-screw and lead-nut system, a linear motor system, an incremental piezoelectric drive system, a hydraulic drive system, a magnetic drive system, or any other suitable drive system. In an alternate embodiment, one or more moving addressing elements are adapted to track to a portion of the display which is being updated. The one or more moving addressing elements may track in response to a pointing device associated with the display, such as a mouse, a touch pad, a track ball, or any other suitable pointing device.
The one or more moving addressing elements may be in the form of one or more strips. Alternatively, the one or more moving addressing elements may be in the form of discs, a series of strips, or other suitable form.
In a further embodiment of the invention, the one or more strips of stationary addressing elements may comprise a continuous sheet electrode arranged on a surface of the first side of the display. In such an embodiment, the one or more moving addressing elements may comprise a series of addressing elements each corresponding to a line of pixels in the array of pixels.
The continuous sheet electrode may be a transparent indium-tin-oxide layer on the inside surface of a transparent substrate.
The addressing elements may comprise either electrodes, brushes, electromagnetic coils, or any other suitable addressing elements. Alternatively, the addressing elements may comprise a series of electrodes on a printed wiring board or any other suitable type of addressing elements.
The display may be a liquid crystal display. In a liquid crystal display embodiment, the pixel actuation field may be an electric field. Alternatively, the display may be a micro-encapsulated liquid crystal display, a micro-encapsulated electro-phoretic display, a twisting ball display, a twisting cylinder display, or any other suitable display.